U.S. patent application number 09/939628 was filed with the patent office on 2002-02-28 for overvoltage-protection device.
Invention is credited to Cantagrel, Michel.
Application Number | 20020024792 09/939628 |
Document ID | / |
Family ID | 8853782 |
Filed Date | 2002-02-28 |
United States Patent
Application |
20020024792 |
Kind Code |
A1 |
Cantagrel, Michel |
February 28, 2002 |
Overvoltage-protection device
Abstract
Overvoltage-protection device, applicable in particular to the
low-voltage mains, comprising, between the two lines (1, 2) of the
mains, a gas-discharge arrestor (3), a varistor (4) and a
thermal-fuse element (5) tasked with ensuring the thermal
disconnection of the device. It includes, in parallel with the
varistor (4), a resistor (7) causing, after the short-circuiting of
the gas-discharge arrestor (3), the heating of the thermal-fuse
element (5) so as to trigger the thermal disconnection of the
device.
Inventors: |
Cantagrel, Michel;
(Houilles, FR) |
Correspondence
Address: |
Burton A. Amernick
Connolly Bove Lodge & Hutz LLP
Suite 800
1990 M Street, N.W.
Washington
DC
20036-3425
US
|
Family ID: |
8853782 |
Appl. No.: |
09/939628 |
Filed: |
August 28, 2001 |
Current U.S.
Class: |
361/127 |
Current CPC
Class: |
H02H 9/06 20130101; H02H
9/042 20130101 |
Class at
Publication: |
361/127 |
International
Class: |
H02H 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2000 |
FR |
00 11015 |
Claims
1. Overvoltage-protection device, applicable in particular to the
low-voltage mains, comprising, between the two lines (1, 2) of the
mains, a gas-discharge arrestor (3), a varistor (4) and a
thermalfuse element (5) tasked with ensuring the thermal
disconnection of the device, characterized in that it includes, in
parallel with the varistor (4), a resistor (7) causing, after the
short-circuiting of the gas-discharge arrestor (3), the heating of
the thermal-fuse element (5) so as to trigger the thermal
disconnection of the device.
2. Overvoltage-protection device according to claim 1, applicable
to the low-voltage mains in a wide range of voltages, characterized
in that the varistor (4) is defined so as to extinguish the
gas-discharge arrestor (3) up to the maximum voltage of use, and in
that the resistor (7) is defined so as to trigger the thermal
disconnection of the device at the minimum voltage of use.
Description
[0001] The invention relates to an overvoltage-protection device,
applicable in particular to the low-voltage mains.
[0002] For the protection of a consumer circuit suplied from the
low-voltage mains (below 400 V, for example), it is usual to use,
between the two lines of a 50 or 60 Hz AC mains, a varistor of
metal-oxide type, especially of zinc-oxide type, mounted in series,
on the one hand, with a thermal-fuse circuit-breaking element, and,
on the other hand, with a gas-discharge arrestor. FIG. 1 represents
a diagram representative of such a device. Between the lines 1 and
2 of the mains, the right-hand part of which is to be protected
against overvoltages, are mounted in series a gas-discharge
arrestor 3, a varistor 4 and a thermal-fuse element 5 subjected to
the tension from a spring 6 tasked with ensuring effective
disconnection after the element 5 blows.
[0003] Such a device theoretically operates in the following way:
the gas-discharge arrestor 3 withstands practically the entire AC
voltage of the mains. In effect, the stray capacitance of the
arrestor 3 is of a few picofarads whereas the stray capacitance of
the varistor 4 is of a few nanofarads. When an overvoltage occurs,
it causes the striking of the gas-discharge arrestor 3, which can
only be extinguished if the current, called secondary current,
which passes through it subsequently becomes sufficiently small. It
is the resistance of the varistor 4 which causes the limiting of
the secondary current and allows the gas-discharge arrestor 3 to be
extinguished.
[0004] When an overvoltage-protection device has operated a certain
number of times, its components reach the end of their lives. In
the case of a gas-discharge arrestor, the end of life corresponds
to short-circuiting. In contrast, in the case of a varistor, the
end of life is manifest as an explosion. As a safety measure, the
gas-discharge arrestor is designed so that its ability to carry
away the energy pulses relating to the overvoltages is less than
that of the varistor. In this way, it is the gas-discharge arrestor
which arrives first at the end of its life and which becomes
short-circuited.
[0005] The voltage of the mains is then transferred fully onto the
varistor 4, which heats up and entails the blowing of the
thermal-fuse element 5 and the thermal disconnection, that is to
say the placing out of service, of the protection device.
[0006] Such a device operates satisfactorily, but only within a
limited range of voltages. This is because, in order for the
varistor effectively to ensure the extinction of the gas-discharge
arrestor, its rated voltage has to be very close to that of the
mains. Moreover, if the rated voltage of the varistor is too high,
the heating necessary to trigger the thermal disconnection will not
be reached and the safety of operation of the device will not be
ensured.
[0007] The object of the invention is to propose an
overvoltage-safety device which can operate in a wide range of
voltages, for example between 180 and 330 V, in order to be able to
fulfill its role in practically all the countries of the world.
[0008] Another object of the invention is to propose an
overvoltage-safety device in which the function of extinguishing
the gas-discharge arrestor is dissociated from the
thermal-disconnection function.
[0009] The subject of the invention is an overvoltage-protection
device, applicable in particular to the low-voltage mains,
comprising, between the two lines of the mains, a gas-discharge
arrestor, a varistor and a thermal-fuse element tasked with
ensuring the thermal disconnection of the device, characterized in
that it includes, in parallel with the varistor, a resistor
causing, after the short-circuiting of the gas-discharge arrestor,
the heating of the thermal-fuse element so as to trigger the
thermal disconnection of the device.
[0010] Advantageously, the overvoltage-protection device is
applicable to the low-voltage mains in a wide range of voltages.
The varistor is defined so as to extinguish the gas-discharge
arrestor up to the maximum voltage of use, and the resistor is
defined so as to trigger the thermal disconnection of the device at
the minimum voltage of use.
[0011] Other characteristics of the invention emerge from the
description which follows, given with reference to the attached
drawing, in which:
[0012] FIG. 1 is a diagram representative of an example embodiment
of an overvoltage-protection device of known type;
[0013] FIG. 2 is an exploded view of an embodiment of a group of
varistors mounted in parallel;
[0014] FIG. 3 is a diagram representative of an example embodiment
of an overvoltage-protection device according to the invention.
[0015] FIG. 2 represents an assembly of four varistors 11, 12, 13,
14 mounted in parallel, separated by electrodes 15, 16, 17 and held
between two strips 18 and 19. Advantageously, the gas-discharge
arrestor is mounted on one of the two strips, and the thermal-fuse
element is mounted on the other.
[0016] In FIG. 3, the same elements as in FIG. 1 bear the same
references. According to the invention, a resistor 7 is mounted in
parallel with the varistor 4. This resistor has a value of a few
hundred ohms, for example 400 ohms.
[0017] In the case in which the varistor 4 consists of an assembly
of several varistors in parallel, as in FIG. 2, one of the
varistors (11) can be replaced by a resistor 7 of the same
dimensions. This resistor 7 may be fixed, or have a negative or
positive temperature coefficient. Its purpose is to cause the
heating which will trigger the thermal disconnection by way of the
thermal-fuse element 5, so as to put the device out of service
after the end of its life, that is to say the short-circuiting of
the gas-discharge arrestor 3.
[0018] Thus, in an intended range of operating voltages between 180
and 330 V, for example, the varistors will be defined so as to
extinguish the gas-discharge arrestor up to the maximum voltage of
use (330 V), while the resistor will be defined so as to be able to
trigger the thermal disconnection at the minimum voltage of the
operating range (180 V).
[0019] The arranging of the resistor 7 in parallel with the
varistor 4 makes it possible to separate the two functions:
extinguishing of the gas-discharge arrestor, and triggering of the
thermal disconnection.
[0020] Throughout the description, the expression gas-discharge
arrestor has been used. This expression also covers the notion of
air-gap arrestor, of surge arrestor or of lightning arrestor.
* * * * *